1. Field of the Invention
The present invention relates to a focus detection device that generates an electric charge based on incoming light through photoelectric conversion.
2. Description of the Related Art
Japanese Patent Application Laid-Open No. 2012-48064 describes a focus detection device that includes a first photoelectric conversion unit and a second photoelectric conversion unit disposed near the first photoelectric conversion unit. The focus detection device described in Japanese Patent Application Laid-Open No. 2012-48064 compares to a threshold the signal level of a signal based on an electric charge of the first photoelectric conversion unit during an electric charge accumulation period for the second photoelectric conversion unit. When the signal level of the signal based on the electric charge of the first photoelectric conversion unit exceeds the threshold, the electric charge accumulation period for the second photoelectric conversion unit is finished. When the electric charge accumulation period is finished, the electric charge accumulated in the second photoelectric conversion unit is transferred through a transfer switch to the input node of an output section that outputs a signal based on the electric charge.
Japanese Patent Application Laid-Open No. 2011-139427 describes a focus detection device that includes a photoelectric converter and a unit cell. The photoelectric converter accumulates an electric charge during an electric charge accumulation period. The unit cell keeps outputting a signal based on the electric charge during the electric charge accumulation period. The focus detection device described in Japanese Patent Application Laid-Open No. 2011-139427 also includes a monitoring unit that compares the signal based on the electric charge to a threshold. In a photoelectric conversion device described in Japanese Patent Application Laid-Open No. 2011-139427, the monitoring unit finishes the electric charge accumulation period for the photoelectric converter when the signal based on the electric charge exceeds the threshold in amplitude.